Technical Field
This disclosure relates to a toner for use in developing an electrostatic latent image. In addition, this disclosure also relates to a developer, and an image forming apparatus, which use the toner.
Description of the Related Art
Recently, a need exists for toner having the following properties:    (1) A relatively small particle diameter so that the toner can produce high quality images;    (2) Good resistance to a high temperature offset problem (hot offset problem);    (3) Good low temperature fixability so that the toner can be fixed at low fixing energy; and    (4) Good high temperature preservability so that the toner can be securely stored or transported at a relatively high temperature after production of the toner.
In particular, since proportion of power consumption in the fixing process in the total power consumption of an image forming apparatus is major, it is important to enhance the low temperature fixability of toner.
In attempting to fulfill the need, a technique in that a crystalline resin is used for the binder resin of toner is proposed. Since a crystalline resin in a crystalline state sharply softens at a melting point thereof, it is possible for a toner using such a crystalline resin to have high temperature preservability at a temperature below the melting point thereof while having a significantly decreased fixing temperature. Namely, the toner has a good combination of low temperature fixability and ability of production of high quality images. However, a crystalline resin having such a melting point that the resultant toner can have good low temperature fixability has good toughness but is soft, and therefore the resin tends to cause plastic deformation. Therefore, toner including only a crystalline resin as a binder resin has poor mechanical durability, and causes various problems such that deformation, agglomeration and fixation of toner occur in an image forming apparatus, and parts of the image forming apparatus are contaminated by the toner.
In attempting to solve the problems, toners including a crystalline resin and a non-crystalline resin as binder resins have been proposed.
In addition, toners using a resin in which a molecular chain (segment) having crystallinity and a molecular chain (segment) having no crystallinity (i.e., amorphousness) are chemically bonded have been proposed. For example, toners using, as a binder resin, a resin in which a crystalline polyester resin used as a segment and a polyurethane used as another segment are bonded have been proposed. Further, a toner using, as a binder resin, a resin in which a crystalline polyester resin used as a segment and an amorphous vinyl polymer used as another segment are bonded is proposed. Furthermore, toners using, as a binder resin, a resin in which a crystalline polyester resin used as a segment and an amorphous polyester resin used as another segment are bonded have been proposed.
Further, a toner including a crystalline resin as a main binder resin and a particulate inorganic material is proposed. In addition, a toner including a crystalline resin having a crosslinked structure formed by an unsaturated bond including a sulfonic acid group is proposed.
Further, a toner which includes a resin including a crystalline polyester resin and a release agent (wax) and in which the crystalline polyester resin and the wax form a sea-island structure (i.e., a phase separation structure) to impart a high level of low temperature fixability to the toner is proposed. Furthermore, a toner that includes a crystalline polyester resin, a release agent and a graft polymer is proposed.
Since the desired level of low temperature fixability of toner becomes higher and higher recently, the above-mentioned toners cannot fulfill the need of such a high level of low temperature fixability.